In a mobile communication device, such as a cellular phone, a power amplifier module is used for amplifying power of a radio-frequency (RF) signal to be transmitted to a base station. In a power amplifier module, a compound semiconductor device including a heterojunction bipolar transistor (HBT) as an amplifier element is used.
In accordance with smaller sizes of recent mobile communication devices, it is also desirable to reduce the size of compound semiconductor devices. In order to satisfy this demand, as disclosed in Japanese Unexamined Patent Application Publication No. 2000-106386, for example, flip-chip mounting may be used instead of wire bonding as a technique for mounting a compound semiconductor device on a module substrate.